Command `act-as-setup` is not documented

**What is wrong with the docs?**
The command `cabal act-as-setup` is not documented.

**Additional context**
```
$ grep -R 'act-as-setup' ./**/*.rst

$ cabal act-as-setup --help
Run as-if this was a Setup.hs

Usage: cabal act-as-setup

Flags for act-as-setup:
-h, --help Show this help text
--build-type=BUILD-TYPE Use the given build type.
```